Search for the K L → π 0 γ decay in the KOTO experiment

Abstract

We report a preliminary result of a new search for the K L → π 0 γ decay, which is forbidden by the Lorentz invariance and gauge principle. The search was carried out using the data obtained from 2016 to 2018 at the J-PARC proton beam facility using the KOTO detector. The achieved single event sensitivity was (6.9 ± 0.3stat. ± 1.5syst.) × 10−8. No signal candidate was found in the signal region and the upper limit was set to B(K L → π 0 γ) < 1.7 × 10−7 at the 90% con dence level.